U.S. patent number 4,622,682 [Application Number 06/593,603] was granted by the patent office on 1986-11-11 for arq transmission system.
This patent grant is currently assigned to Ricoh Company, Ltd.. Invention is credited to Kazumasa Kumakura.
United States Patent |
4,622,682 |
Kumakura |
November 11, 1986 |
ARQ transmission system
Abstract
A facsimile communication system equipped with an ARQ function
for transmitting data in the form of a block between a transmitter
and a receiver through a transmission route having a relatively
large time delay, such as a submarine cable and communications
satellite, is provided. In the system, prior to transmission of
image data, a time delay in transmission of data through a selected
transmission route is measured and the number of bits of data block
is determined in accordance with the thus measured time delay.
Inventors: |
Kumakura; Kazumasa (Sagamihara,
JP) |
Assignee: |
Ricoh Company, Ltd.
(JP)
|
Family
ID: |
12811295 |
Appl.
No.: |
06/593,603 |
Filed: |
March 26, 1984 |
Foreign Application Priority Data
|
|
|
|
|
Mar 25, 1983 [JP] |
|
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58-48726 |
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Current U.S.
Class: |
375/285; 178/69R;
714/748 |
Current CPC
Class: |
H04L
1/16 (20130101) |
Current International
Class: |
H04L
1/16 (20060101); H04L 001/16 () |
Field of
Search: |
;375/37,40,58
;371/2,30,32 ;370/82,83 ;358/256,263,257 ;178/63R,63E,69R,69M,23A
;455/63,68,69 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Safourek; Benedict V.
Attorney, Agent or Firm: Shoup; Guy W.
Claims
What is claimed is:
1. A communication system having an ARQ function for transmitting
data between a transmitter and a receiver in which said receiver
supplies a response signal to said transmitter every time said
receiver receives a block of data having a predetermined number of
bits from said transmitter, said system comprising:
delay measuring means for measuring a time delay in transmitting a
signal between said transmitter and said receiver through a
selected transmission route;
means for generating and transmitting said block of data to be
transmitted from said transmitter to said receiver; and
controlling means responsive to said time delay measured by said
delay measuring means for controlling said means for generating and
transmitting such that said number of bits of said block of data is
varyingly set in accordance with said time delay measured by said
delay measuring means wherein said response signal from said
receiver is different in frequency from said data transmitted by
said transmitter.
2. The system of claim 1 wherein said number of bits of said block
of data is increased by said controlling means as said time delay
increases.
3. The system of claim 1 wherein said number of bits of said block
of data is varied as an integer multiple of a reference number in
accordance with a magnitude of said time delay measured by said
delay measuring means.
4. The system of claim 1 wherein said system is a facsimile
communication system which includes a delay causing element causing
a relatively large delay in data transmission in a communication
route between said transmitter and said receiver.
5. The system of claim 4 wherein said delay causing element is a
submarine cable or a communications satellite.
6. The system of claim 4 wherein said system is equipped with an
ARQ function.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a data transmission system and
particularly to a facsimile transmission system in which a receiver
can send a request for retransmission of data in the form of a
block upon detection of an error to the transmitter.
2. Description of the Prior Art
As well known in the art, in a facsimile communication system, in a
protocol procedure prior to transmission of messages or image data,
the transmission speed or rate of MODEM is selected to carry out
MODEM training, and if successful, transmission of image data at
the selected transmission speed is carried out. However, even if
the MODEM training has been carried out successfully, it does not
insure the transmission of image data in an excellent condition at
all times. If the condition of transmission line becomes poor
during a transmission operation, image data may be partly lost
during transmission thereby hindering to transmit image data in a
complete form to a receiver.
In order to cope with the above-described inconveniences, the ARQ
method has been applied to a facsimile transmission system. In this
case, image data is divided into blocks, each containing a
predetermined number of bits, prior to transmission to a receiver.
And, to each block data is added a start flag, stop flag, command (
including block number ) and CRC code so that the image data is
formulated into a predetermined frame. Thus, the image data is
transmitted from a transmitter to a receiver block by block. At the
receiver, each block data is examined upon receipt and if it is
found that there is abnormality in CRC code, the block number
differs from the one expected at the receiver, and/or the flag is
destroyed, then the receiver automatically sends a signal for
requesting retransmission of block data to the transmitter.
In such a scheme, the same image data is repetitively transmitted
from the transmitter to the receiver whenever malfunction occurs
during transmission. Thus, it is insured that the image data
received at the receiver is always normal without loss and
alterations, thereby allowing the receiver to receive an image
which is faithful to an original image transmitted from the
transmitter at all times. In a transmission system equipped with
such an ARQ function, the transmitter must receive a response
signal from the receiver while the transmitter is transmitting the
next following block data. Therefore, the above-described ARQ
function becomes inoperative when data must be transmitted through
a transmission route having a relatively large delay in
transmission. For example, this happens when a submarine cable or
communications satellite is involved. When a submarine cable is
used, there is a transmission delay of approximately 50
milliseconds in one way; whereas, when a communications satellite
is used, there is similarly a transmission delay of approximately
300 milliseconds. In such a case, since there is a relatively large
delay in transmission, there is a chance that the transmitter fails
to receive a response signal from the receiver as to the last
preceding block data which has been just transmitted while the
transmitter is transmitting the next following block data.
SUMMARY OF THE INVENTION
It is therefore a primary object of the present invention to
provide an improved data transmission system.
Another object of the present invention is to provide a data
transmission system provided with an ARQ function which may remain
operative even if there is a relatively large delay in
transmission.
A further object of the present invention is to provide a facsimile
transmission system capable of transmitting image data without loss
and/or alterations.
A still further object of the present invention is to provide an
ARQ equipped facsimile communication system which allows to
transmit image data through a transmission route having a
relatively large transmission delay, such as a submarine cable and
communications satellite.
Other objects, advantages and novel features of the present
invention will become apparent from the following detailed
description of the invention when considered in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing the overall structure of an
ARQ-equipped facsimile communication system constructed in
accordance with one embodiment of the present invention; and
FIGS. 2(a) through 2(d) are timing charts showing several wave
forms which are useful for understanding the operation of the
system shown in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, there is shown an ARQ-equipped facsimile
communication system constructed in accordance with one embodiment
of the present invention. As shown, the system includes a
transmitter 1, a receiver 2 and a transmission line L extending
between the transmitter 1 and the receiver 2. The transmitter 1
includes a transmission controller 11 which carries out the overall
transmission control of transmitter 1, a low speed MODEM 12 for use
with various control signals and a high speed MODEM 13 for use with
image data to be transmitted. Similarly, the receiver 2 includes a
reception controller 21, a low speed MODEM 22 and a high speed
MODEM 23.
The transmitter 1 further includes a block data generator 14 as
connected to the transmission controller 11 and high speed MODEM
13. The block data generator 14 receives compressed image data line
by line and stores the data temporarily, and, then, divides the
data into blocks each having a predetermined number of bits set by
the transmission controller 11. Then a start flag, a stop flag, a
control bit and a CRC code are added to each of the block data thus
formed and the block data added with additional information are
supplied to the high speed MODEM 13.
The transmitter 1 also includes a response signal detector 15
connected to the transmission line L for detecting a reception
response signal indicating the safe receipt of a block of data by
the receiver and a block data generator controller 16 for
controlling the operation of the block data generator 14 such that
the next following block of data is transmitted if the received
response signal indicates ACK (acknowledgment) and, on the other
hand, the same block of data is retransmitted if the received
response signal indicates NACK (non-acknowledgment). Moreover, in
response to a command supplied from the transmission controller 11,
the block data generator controller 16 also functions to stop input
of image data into the block data generator 14.
Also provided in the transmitter 1 is a delay measuring signal
generator 17 connected to supply a delay measuring signal for
measuring a time delay of a transmission route to the transmission
line L. The transmitter 1 also includes a delay response signal
detector 18 for detecting a delay response signal transmitted from
the receiver 2 in response to the delay measuring signal and a
delay measurement controller 19 which activates the delay measuring
signal generator 17 and receives a detection signal from the delay
response signal detector 18 to measure a time delay in transmitting
data between the transmitter 1 and the receiver 2 through the
transmission line L.
On the other hand, the receiver 2 includes a data input circuit 24
which decomposes the frame of received data and to store the
resulting image data and an error detector 25 which calculates a
CRC code on the basis of the received data and to compare the
calculated CRC code with the transmitter-added CRC code of the
received data, whereby the error detector 25 supplies as its output
an ACK (acknowledgment) detection signal if agreement is found
between the two CRC codes or a NACK (non-acknowledgment) detection
signal if no agreement is found. There is also provided an input
control circuit 26 as connected between the data input circuit 24
and the error detector 25. The input control circuit 26 controls
the operation of the data input circuit 24 such that the data input
circuit 24 supplies image data to the next following stage only
when the error detector 25 supplies an ACK detection signal and
there is an agreement between the block number in the control frame
and the block number expected at the receiver 2. Also provided is a
response signal generator 27 which supplies an appropriate response
signal to the transmission line L depending upon the contents of a
detection signal supplied from the error detector 25.
The receiver 2 also includes a delay measuring signal detector 28
for detecting the delay measuring signal transmitted from the
transmitter 1 through the transmission line L and a delay response
signal detector 29 which supplies a delay response signal to the
line L in response to a detection output supplied from the delay
measuring signal detector 28.
It is to be noted that the above-described response signals are
signals in a frequency band, e.g., 330 Hz or 3,300 Hz, which is
different from the frequency band in transmitting facsimile
signals. Thus, even during transmission of image data, image data
and response signals may be transmitted at the same time using the
same transmission line L.
When a facsimile communication is to be carried out with the
above-described structure, prior to entering into a predetermined
communication control procedure, the transmission controller 11 of
transmitter 1 supplies a command signal to the delay measurement
controller 19 to activate the delay measuring signal generator 17.
Thus, a delay measuring signal shown in FIG. 2(a) is supplied to
the transmission line L and then after elapsing a time period
t.sub.1 it is detected by the delay measuring signal detector 28 of
the receiver 2, as indicated by FIG. 2(b). At the falling end of
the delay measuring signal, the delay measuring signal detector 28
apprises the delay response signal detector 29 of the fact that the
delay measuring signal has been detected. And, thus, the delay
response signal detector 29 supplies a delay response signal to the
transmission line L. This delay response signal is detected by the
delay response signal detector 18 of the transmitter 1, as
indicated by FIG. 2(d), and the delay response signal detector 18
apprises the delay measurement controller 19 of the fact that the
delay response signal has been detected.
Now, time t from activation of the delay measurement controller 19
by the delay measuring signal generator 17 to detection of the
delay response signal by the delay response signal detector 18 is a
sum of transmission delay time t.sub.1, t.sub.2, signal width
t.sub.3 of delay measuring signal and processing time t.sub.4 at
the receiver 2. Among these various time periods, signal width
t.sub.3 is a previously determined value and the processing time
t.sub.4 is also a predetermined value, so that the total time delay
T.sub.d may be expressed as follows:
Accordingly, after measuring time t, the delay measurement
controller 19 carries out the above-described calculation to obtain
a total delay time T.sub.d, which is then output to the
transmission controller 11. In response to the received total delay
time T.sub.d, the transmission controller 11 determines the number
n of bits in a block of data, for example, according to the
following table, which is then supplied to the block data generator
14.
______________________________________ Total Delay Time No. of Bits
______________________________________ T.sub.b < T.sub.s /2 N
T.sub.s /2 .ltoreq. T.sub.b < T.sub.s 2N T.sub.s .ltoreq.
T.sub.b < 3T.sub.s /2 3N 3T.sub.s /2 .ltoreq. T.sub.b <
2T.sub.s 4N ______________________________________
In the above table, N is an integer indicating a reference length
of a block of data, e.g., 2,048, and T.sub.s is time required to
transmit the data having N number of bits.
After determining number N of bits of a block of data in this
manner, the transmitter 1 enters into a predetermined communication
procedure to carry out transmission of image data as well known for
one skilled in the art.
It is to be noted that a relation between time T.sub.d and number N
of bits should not be limited only to the above-described table.
What is critical here is that the system allows the transmitter to
receive a response signal supplied from the receiver while the
transmitter is transmitting the next following block of data. It is
also to be noted that the measurement of delay time T.sub.3 may
also be carried out during the facsimile communication procedure.
In this case, use may be made of optional signals in the procedure,
such as NSS as a delay measuring signal and CFR as a delay response
signal. It should also be noted that the above-described embodiment
is a case in which the present invention is applied to a facsimile
communication system; however, the present invention may also be
applied to other data communication systems employing the ARQ
function.
As described above, in accordance with the present invention, the
transmission time delay is first measured and the number of bits of
a block of data to be transmitted is determined depending upon the
measured time delay, so that the ARQ function may be maintained
operative even if there is a relatively large time delay in a
selected communication route.
While the above provides a full and complete disclosure of the
preferred embodiments of the present invention, various
modifications, alternate constructions and equivalents may be
employed without departing from the true spirit and scope of the
invention. Therefore, the above description and illustration should
not be construed as limiting the scope of the invention, which is
defined by the appended claims.
* * * * *